How can the change of one Proton, or Electron in a
single atom, change the physical properties of it?
How to these charges stay together, without
floating away from the nucleus?

Question Date: 2018-11-02

Answer 1:

First of all, in any atom, the number of
protons in the nucleus must equal the number of
electrons out side of the nucleus. And the
behavior of the electrons must obey a series of
rules under quantum mechanics. There is
one particular rule of quantum mechanics called
"Pauli's exclusion principle", this means
that any two electrons cannot have exactly the
same behavior in an atom. This directly leads
to the fact that adding one electron (also one
proton) to the atom can potentially drastically
change the property of the atom, because this
one extra electron has to behave totally
differently from all the other electrons, due to
the Pauli's principle.

The protons all carry positive charge, so it is
hard to imagine how they can all stick together
instead of pushing each other away in a nucleus.
Indeed, the Coulomb force dictates that the
same charges repel each other. However, the
protons also have what is called the "strong
force" between each other. And it is the
strong force that holds all the protons
together (actually the strong force holds
together all the protons with many neutrons in a
nucleus). The size of a nucleus is extremely small
(roughly 1/100000 of an atom), at that length
scale, the strong force will dominate the Coulomb
interaction. But strong force is a very
short-range force, beyond the scale of the
nucleus, strong force can be ignored. While the
Coulomb force is a long range force. So in our
daily life the strong force is negligible, we
only need to worry about the Coulomb force.

By the way, there are four so called fundamental
forces in our universe: gravity,
electromagnetic force (more general version of the
Coulomb force), strong force, and weak force.
The first two (gravity and Coulomb forces) are
long range forces, this is why they dominate most
of the phenomena in our life; the strong and weak
forces are very short range forces, they will not
play a role unless we study very tiny objects
like nucleus.

Answer 2:

Changing the number of protons in an atom is
important to the properties because it changes the
number of electrons in the stable configuration of
the atom. This is because the properties of
an atom are determined by the way it interacts
with other atoms. The interactions occur through
chemical
bonds, which are intimately linked to the
number of electrons. Bonds form when doing so
is
energetically favorable . Adding or removing
electrons will change the nature of the bonds
which form (or even make formation of bonds
unfavorable ), thereby changing the
properties. An important point is that it is
(primarily) the electrons in the outer shell which
are involved in bonding. Combining this with
the previous information, one might expect that
atoms with the same number of electrons in their
outer shell
("valence electrons") to have similar
properties. In fact,
this is the case - columns of the periodic
table are called "groups" because the
elements within them tend to have very similar
properties, and this stems from their having the
same number of valence electrons and thus forming
similar bonds.

There are differences between elements within a
group though, and these are also typically
related to the number of electrons. Here it
is the total number of electrons though, not just
the number in the outer shell. For example,
boiling points tend to increase with
atomic number (i.e., with number of protons,
moving down a column). This is because the
attractive forces holding the atoms
together (
Van der Waals forces , comprising
dipole-dipole and London dispersion forces) are
related to the average position of the
electrons. With a larger number of
electrons, larger dipoles can be created, thus
causing stronger attractions and increasing the
energy needed to pull them apart.

The second question, about electrons staying
near the nucleus is a bit tricky. The main answer
is that electrons are kept near the nucleus due
to electromagnetic interactions - the negative
charge of the electron is attracted to the
positive charge of the proton. However, there are
some other considerations/complications. The
common picture of atoms (a holdover from the early
days of atomic physics) is one in which
electrons orbit the nucleus , much like
planets around a sun. This model has
plenty of
issues , but the end result is that it is
better to consider electrons to be a sort of
distribution around the nucleus rather than a
particle with an identifiable proton.

Answer 3:

Opposite electric charges exert a force that
draws them together. Protons carry one unit
of positive charge, while electrons carry one unit
of negative charge. Thus an atom with more protons
than electrons will have a net positive charge and
attract electrons until the protons and electrons
are equal in number and the atom has a total
charge of zero.

Answer 4:

A force called the strong force holds
neutrons and protons together in the
nucleus. Electrons are held near the nucleus due
to the attraction between the
positively charged protons and negatively charged
electrons. When a proton is
added to an atom, it makes the nucleus more
massive — a proton is nearly
10000x as massive as an electron. This causes
the element to weight more.

The increased positive charge also causes the
electrons to be more attracted
to the nucleus. If an electron is added, the
electron cloud which surrounds the
nucleus becomes bigger, and the atom has more
electrons with which to
interact with its surroundings. This means it can
bond to other atoms, or distort
the electron clouds of nearby atoms. Physical
properties like boiling point,
freezing point, and even the color of the element
all have to do with how much
the nucleus weighs, and how the electrons are
interacting with the
environment. The exact interactions are generally
very complex, but you can
imagine that when you have a lot of atoms - most
every day examples of
chemical systems contain on the order of
10(23) atoms - one more electron on
each atom can make a big difference!